In an etching process of a manufacturing process of a semiconductor device or a flat panel display (FPD), a film on a surface of a substrate to be processed (a semiconductor wafer, a glass substrate or the like) is processed in a desired circuit pattern by using as a mask a resist pattern formed by a lithography technique. Conventionally, a capacitively coupled plasma etching apparatus has been widely used for single-wafer etching.
Generally, in a capacitively coupled plasma etching apparatus, an upper electrode and a lower electrode are arranged in parallel in a vacuum processing, and a substrate to be processed is mounted on the lower electrode. By applying a radio wave power between the electrodes, a radio wave electric field is generated between the electrodes. Then, molecules of a processing gas are ionized by collision with electrons accelerated by the radio wave electric field, electrons emitted from the electrodes, or heated electrons, thereby generating a plasma of the processing gas. Accordingly, desired micro-machining, e.g., etching, can be performed on a surface of the substrate by radicals or ions in the plasma.
As the size of semiconductor device is scaled down, a requirement for a shape and a dimensional accuracy in plasma etching becomes stricter. Conventionally, a film deposited or formed on a sidewall of a resist or a pattern during an etching process is used as a so-called sidewall protection film to control an etched cross sectional shape. When a deposition rate is high, the sidewall of pattern is protected from neutral reactive species or ion impact, so that an undercut or a bowing hardly occurs. If the deposition rate is too high, an etching rate decreases. This may cause an excessively tapered shape or even results in the stop of etching reaction. In addition, as the etching time increases, the resist may be deteriorated of consumed a lot, resulting in the dimensional inaccuracy.
Therefore, in order to improve accuracy of anisotropic processing by preventing generation of undesired bow or taper shape, it is required to properly combine an etching dominant process and a deposition dominant process. For that reason, conventionally, there is employed a multi-step method, wherein a single continuous etching process is divided into a plurality of steps in accordance with the chemistry of an etching gas, such that the etching dominant step, in which an etchant gas for enhancing etching is supplied into the chamber, and the deposition dominant step, in which an etchant gas for facilitating deposition is supplied into the chamber are carried out sequentially.
However, the conventional multi-step method in which different etching gases are used in a plurality of steps requires a plurality of gas supply sources, so that the etching apparatus is scaled up. Further, transition between the etching dominant step and the deposition dominant step is stepwise and discontinuous. As a consequence, a stepped portion may be generated on the pattern sidewall, and it is difficult to control a desired etching shape accurately.